The invention discloses a method for evaluating a system damping ratio based on the number of power oscillation times. According to the method, a small interference linearity equation of the interconnected network is generated based on data provided by a wide domain measuring system and power system analysis comprehensive program software, and the equation is solved to obtain time domain expressions of the power oscillation of various branches; the number of effective disturbance times of connecting lines between two domains within the domain oscillation frequency range and the relation of the theoretical ratio of the total number of effective disturbance times of the interconnected network and the damping ratio among the domains are obtained according to the time domain expressions of the power oscillation of the branches and an effective disturbance judging method; the number of effective daily disturbance times among the domains and the number of effective daily disturbance times of the interconnected network are obtained through the wide domain measuring system, and the actual ratio of the number of effective daily disturbance times among the domains and the number of effective daily disturbance times of the interconnected network is worked out; a curve chart corresponding to the relation is drawn, and the evaluation value of the damping ratios among the areas is obtained. The value of the damping ratio of the system and the changing situation can be evaluated according to WAMS historical data, and reference data are provided for operation workers.